Salinity reduces growth, gas exchange, chlorophyll and nutrient concentrations in diploid sour orange and related allotetraploid somatic hybrids
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Diploid seedlings of sour orange (SO) (Citrus aurantium (L.)) (2x) and allotetraploid (4x) somatic hybrid plants of SO with Carrizo citrange (SO+CC) (Citrus sinsensis x Poncirus trifoliata), Palestine sweet lime (SO+PSL) (Citrus aurantifolia. (Christm.) Swing) and Flying dragon (SO+FD) (Poncirus trifoliata), were grown under greenhouse conditions and irrigated with nutrient solution containing 0, 60, or 90 mM NaCl. Net gas exchange and leaf Cl concentration were measured 21, 28 and 35 d after beginning the salinity treatment. At the end of the experiment (day 35), Ca, Mg, K, total N and P concentrations in leaves and roots, growth parameters and chlorophyll concentrations were measured. Diploid plants of sour orange (SO) accumulated less Cl and Na in leaves than did the tetraploid plants. However, Cl and Na concentrations in roots were similar or higher in SO than in tetraploid plants. At day 35 in the 60 mM treatment, accumulation of salts in leaves was negatively correlated with growth. Thus, SO was more salt tolerant than the tetraploids and SO+PSL was the least tolerant to salinity. After 35 d, salinity reduced leaf chlorophyll, photosynthesis, stomatal conductance and whole plant transpiration in all selections. Salinity decreased the concentration of K in leaves and roots but increased the concentration of tissue N. At 90 mM NaCl, there was no correlation between Cl and Na accumulations in leaves and shoot fresh weight reduction.
